Agricultural crop producers routinely apply liquid fertilizer to crop fields to replenish depleted nutrients beneficial to crop production. A common fertilizer used to replenish nitrogen in the soil is anhydrous ammonia (“NH3”). An applicator may include a plurality of selectively spaced “knives” or “shanks,” which may be pulled through the soil at a selected depth, typically behind a farming tractor. A fertilizer application line may be positioned immediately behind each knife and extend nearly to the knife tip to release a selected amount of fertilizer into the soil as the knife is pulled through the soil. A disc may follow behind each knife and turn the soil to seal in the NH3 so it can mix with soil moisture to provide nitrogen to growing crops.
Fertilizer type and application rates may vary depending upon crop type. NH3 application rates may range from less than 40 pounds per acre to in excess of 200 ponds per acre. Applicators may include as few as 8 knives to in excess of 40 knives, and may be arranged across an applicator tool bar spanning a width of over 50 feet.
In a common arrangement, the bulk NH3 may be provided in a pressurized tank or “nurse-bottle” pulled behind the applicator. One or more high pressure hoses may function as a supply line to conduct NH3 from the nurse-bottle to one or more distributors.
The distributor may manifold the NH3 from a single supply line to each of a plurality of applicator lines, with each applicator line positioned substantially adjacent and behind a knife. NH3 may be conducted to the distributor through an inlet port positioned substantially within the center of an array of outlet ports. Unused ports may be plugged. The supply line, the applicator lines and the distributor may include a number of fittings, valves, obstructions, and changes of flow-direction, each of which may create a tortuous flow path and resultant pressure drops along the flow path.
Accurate and even application of anhydrous ammonia over the length of the applicator tool bar has been a significant problem which the farming industry has struggled to solve for many years. The fluid-phase state of NH3 is sensitive to each of pressure and temperature. NH3 may exist in a gas or vapor phase, a liquid phase, or both, depending upon the pressure and temperature conditions. Pressure drops may result in generation and/or expansions of a vapor phase. The vapor phase may consume a relatively high percentage of the available conduit volume and may be much more mobile or conductive, and thus more difficult to meter or control than the liquid phase. Devices commonly used to measure and divide the liquid to each knife may work well in a homogenous fluid streams, but may not perform well when random vapor pockets traveling within the liquid stream are encountered. Pockets of vapor may severely retard or impede liquid flow and/or measurement uniform distribution of anhydrous ammonia.
To provide greater distribution and application control and rate consistency between the knives, it is commonly more desirable to distribute liquid NH3 with no vapor to each of the application lines. The presence of a vapor phase within the distribution system may result in significant rate variability between knives. For example, some knives may be receiving two to four times more NH3 than other knives. Thereby, some crops may risk being burned, while others may be starved for nitrogen, the results of which may show up in crop yield, color and/or quality.
A number of products have been developed to improve liquid fertilizer distribution. One general group of distributors operates by generating a cyclone to create a vortex within the distributor and utilizes a vertical dam to segregate the liquid phase from the vapor phase. One such device is marketed by Continental NH3 Products, and is commonly referred to as a vertical dam manifold, as described in U.S. Pat. No. 5,372,160. The device may utilize interchangeable distribution rings that differ in the number of outlet holes and in the size of the outlet holes. In theory, one side of the dam is flooded with liquid while the other side of the dam contains the vapor phase. The liquid phase portion of the fertilizer is distributed to each of the plurality of applicator line outlets in an attempt to provide substantially equal rates of liquid to each applicator line. The vapor is allowed to rejoin the liquid streams downstream of the liquid distribution. A fluid back pressure is preferably maintained upstream of the distribution ring, thereby maintaining a reduced vapor phase. A distributor providing small outlet ports may be required for low application rates, while a different distributor having larger outlet port sizes may be required for higher application rates. Although improved results may be obtained with such product as compared to more conventional distributors, results may reflect average application rate differences between knives in excess of 15% from the mean rate. Other devices using the cyclonic or spray principle are disclosed in U.S. Pat. No. 4,807,663, issued to Jones, and U.S. Pat. No. 4,284,243, issued to Shaner.
A second general group of prior art distributors uses rotors to mix or homogenize the two-phases into a mixture. U.S. Pat. No. 6,003,532 discloses a device that attempts to homogenize the two-phase vapor-liquid stream prior to distribution. The device uses a rotating flywheel driven by the incoming fluid to spin at a high velocity and sweep the incoming fluid rapidly past evenly spaced output holes on the inner surface of a distribution ring. The rapid sweeping action ideally homogenizes the mixture and thereby uniformly distributes the fertilizer. A desirable back-pressure is maintained by utilizing a distribution ring having appropriately sized outlet holes. Another device using the rotor technique is disclosed in U.S. Pat. No. 5,333,640, issued to Swift. Multiple distribution rings are thus generally required for a diversity of application ranges. Another drawback to this design is wear and maintenance of additional moving parts.
A third type of distributor utilizes a pump to increase fluid pressure in the distributor prior to distribution. Pressure may be increased to a level such that the pressure at each exit nozzle behind a respective knife may be greater than tank pressure at each exit nozzle behind a respective knife may be greater than tank pressure. For example, injection pressure may be 150 psig, while tank pressure may be less than 120 psig. Thereby, the NH3 may remain in a liquid phase as it is conducted from the tank, through the system to the exit nozzle. Some additional pressure may be required to account for NH3 temperature increases within the system. The distributor may include a first arrangement of small-diameter distributor orifices that provide an appropriate regulation of rate at low application rates and speeds. A piston may be provided to move in response to increased pump pressure and/or applicator speed, exposing a second arrangement of distributor orifices having slightly larger diameters. Thereby, for a particular injection pressure the application rate may be increased. Such distributor system may be relatively expensive and maintenance intensive, requiring relatively complicated machining and expensive tooling on the piston, manifold and orifices. In addition, the pump is required, including means for powering, positioning, controlling, and maintaining the pump.
An improved method and system is desired for distributing liquid fertilizers substantially equally across the applicator bar. An improved method is desired which is economical and may be effective across a broad range of application rates and pressures without need for purchasing additional distributor equipment or pumps. The disadvantages of prior art are overcome by the present invention.